ABSTRACT—Sustainability has become an important issue to the aluminum industry in recent
years. Environmental regulations have become more stringent, and societal pressures to reduce
the environmental footprint of our operations have increased. In U.S. casthouses, Secondary
MACT regulations set specific limits on gaseous and particulate emissions from furnaces and inline
metal treatment units. Chlorine gas is often used in furnaces and in-line to remove alkali and
alkaline earth impurities, enhance flotation of inclusions, and dry the dross. Alcoa has made
steady progress over the last twenty years to reduce or eliminate the use of chlorine gas in metal
treatment, while maintaining metal quality and meeting environmental regulations. This progress
can be characterized as a series of step changes in technology, both in processes and in
equipment. These changes have included mixed gas tube fluxing, bagged salt addition, bath
carryover reduction, rotary gas fluxing, rotary salt fluxing, and in-line salt injection. The
effectiveness of these methods and their impact on emissions levels will be summarized.